1. Field of the Invention
The present invention relates to a combination magazine and shipping tray for lead frames cut into discrete length strips.
2. Description of the Prior Art
Lead frames are used in the packaging of semiconductor integrated circuits (ICs). Referring to FIG. 1, a discrete length strip of lead frames according to the prior art is shown. The discrete length strip 10 includes a plurality of lead frames 12 mechanically connected by a frame 14. Each lead frame 12 includes a plurality of leads 16 and a die pad area 18. With high lead count lead frames, a tape 20 may be applied across the leads 14 to prevent bending or displacement of the leads 16. The die pad area 18 is usually downset from the plane defined by the leads 16 so that when a die is placed on the pad area 18, it is substantially co-planar with the leads 16 of a lead frame 12. A plurality of indexing holes 22 in the frame 14 are used for indexing the discrete length strip 10 through machines used to package ICs. The discrete length strips 10 (hereafter "discrete strips") generally contain from 5 to 20 lead frames 12 per discrete strip 10, depending on the size of the individual lead frames 12.
Discrete strips 10 are mass produced from a long narrow strip of metal, such as copper or "alloy 42", which is selectively stamped. Each stamp forms a pattern of a lead frame 12 with the leads 16 and the die pad area 18. The peripheral regions of the strip of metal form the frame 14 which holds the individual lead frames 12 together. The strip of lead frames 12 is usually rolled onto a reel, and spot plated in a reel to reel selective plating system. For examples of a selective plating system, see U.S. Pat. Nos. 3,746,630 and 3,723,283, which are assigned to the assignee of the present invention. In subsequent steps, the tape 20 may be applied to the leads 16 and the die area 18 may be downset. The long selectively plated strip of lead frames is then cut into the discrete strips 10, as illustrated in FIG. 1.
The machines used to package integrated circuits are designed to operate on a lead frame 12 in the form of a discrete strip 10. In the packaging of semiconductor devices, a discrete strip 10 is loaded into a series of packaging machines to complete the packaging of the ICs. First, the discrete strip 10 is fed into a die attach machine where a die is fixed to each of the die pad areas 18. In a bonding machine, the leads 16 are electrically bonded to the die of each lead frame 12. In an encapsulation machine, the leads 16 and die of each lead frame 12 are then encapsulated in a packaging material, such as plastic or ceramic. The individual packages are then excised from the frame 14 of the discrete strip 10 to complete the IC packaging process.
Prior to shipment of the lead frames to a packaging facility, the discrete strips 10 are inspected for defects. Referring to FIG. 2, a block diagram of a lead frame quality inspection station, such as Model No. Spectra 2000 manufactured by Electrical Plating Engineering Company, is shown. The station 30 includes an automatic quality inspection machine 32, a conveyor 34 including a plurality of rollers 36A and 36B for conveying discrete strips 10, a reject bin 38, an accept bin 40, an unload elevator 42 positioned inside the accept bin 40, an optical sensor 43 and a packaging tray 44.
The rollers 36A and 36B operate independent of one another, but both under the control of the inspection machine 32. In response to a signal from inspection machine 32, the rollers 36A may be horizontally withdrawn from their normal operating position. As a result, a discrete strip 10 on the rollers 36A is dropped into the reject bin 38. Similarly, in response to another signal from the inspection machine 32, the rollers 36B may be horizontally withdrawn from their normal operating position. As a result, a discrete strip 10 on the rollers 36B is dropped into the accept bin 40.
During operation, discrete strips 10 are fed into the inspection machine 32 where they are inspected for defects. The inspected discrete strips 10 are placed onto conveyor 34 where they are conveyed toward the accept bin 40. If a discrete strip 10 is defective, however, the inspection machine 32 transmits a control signal to the rollers 36A. The defective discrete strip 10 is then dropped into and discarded in the reject bin 38 before it reaches the accept bin 40. Alternatively, if a discrete strip 10 passes inspection the inspection machine 32 directs the discrete strip 10 to be conveyed beyond the reject bin 38. At the accept bin 40, the inspection machine 32 transmits a control signal to the rollers 36B and the discrete strips 10 fall onto the unload elevator 42 in the accept bin 40.
As the discrete strips 10 accumulate into the accept bin 40, the unload elevator gradually descends. The optical sensor 43 determines the number of discrete strips 10 in the accept bin. Once a predetermined number of discrete strips 10 are accumulated in the accept bin 40, for example one hundred, the inspection machine 32 is shut off. The discrete strips 10 are then manually removed from the unload elevator 42, bundled, wrapped in paper, and placed by hand into the packaging tray 44.
A complete description of the packaging tray 44 is described in U.S. Pat. No. 4,798,305, entitled "Adjustable Shipping Tray", and is assigned to the assignee of the present invention. The adjustable shipping tray 44 provides a flat bottom, two sets of opposing vertical sides and an open top. Within the tray, one or more movable partitions are provided to allow the internal compartment of the tray to accommodate the bundles of lead frames of different sizes and configuration.
The prior art method of manually removing, wrapping and packing bundles of discrete strips 10 into the adjustable tray 44 has a number of deficiencies. First, manual handling of the lead frames may cause physical damage to the delicate discrete strip 10. The plated surfaces of lead frames may become scratched, leads 16 may be displaced, or the discrete strip 10 may be bent if mishandled. Second, the surface area of the lead frames 12 may be contaminated if the person manually handling the lead frames has dirty hands.